An air bag comprises an inflatable bag and means for inflating the bag. Air bags are highly desired life saving devices that have performed well in many accidents and saved many lives. However, the bag must be inflated in a very brief time such as 1/30 of a second which requires rapid movement of the bag from a stored and compacted state to a fully inflated state. The rapid deployment of the bag involves great force. A deploying bag can injure a person during the early phases of deployment if the person is very close to where the airbag is stored. Another hazardous circumstances is when the occupant is a baby in a rear-facing baby seat. It is also desired to inhibit deployment if there is no person in the seat. Much effort has gone into developing systems for characterizing the occupant and ascertaining the occupant position to meet this need. Proposed systems attempt to ascertain the distance from the inflator to the occupant and systems using sonic and optical ranging for that purpose are well known. These systems are deficient in that they cannot reliably distinguish between an occupant and other things such as road maps, beverage cups, packages and voluminous clothing which cause indications that the occupant is near the inflator. Known prior art systems operate to measure the distance from the inflator to the occupant, presumably because that is the physical variable most easily related to the potential for injury.
Many vehicles include an accelerometer located in the passenger compartment for sensing the deceleration of a crash. These accelerometers are incorporated in sensing and diagnostic modules or "SDM" which are decision making centers for the vehicle occupant protection system. The output of the accelerometer may be integrated by an analog circuit or a microprocessor in the SDM to compute a difference between the velocity the vehicle was traveling before a crash and the velocity of the passenger compartment during the crash. The integral of the accelerometer output may be integrated again to obtain the second integral of the deceleration which is the displacement of a free body from its initial position relative to the vehicle. An occupant not wearing a seat belt is, to a good approximation, a free body. Therefore, this calculation provides the distance an unbelted occupant has moved from his or her initial position at any time during the crash. Vehicles typically include seat belt latched sensors for indicating seat belt usage.
Position and angle sensors are in commercial production for sensing the position of a seat on its track and the angle the seat is reclined.
Capacitive proximity sensors have been well known for many years and have many successful applications. In addition to measuring capacitance, the Q of the capacitance may be used to provide additional information about the nature of the material being detected. Some materials including materials containing water tend to reduce the Q of the sensed capacitance.
Circuits for measuring capacitance and the Q of a capacitor are well known and are incorporated in many commercially available measuring instruments.
A general object of this invention is to provide an occupant position sensing means and associated decision making for automotive vehicles which also overcomes certain disadvantages of the prior art.